Introduction
In the ever-evolving world of winemaking, where tradition meets innovation, ecological transition is a vital factor in shaping practices and processes. An integral part of this shift towards sustainability is the valorization of by-products, which is essential for carbon neutrality. One such byproduct, often overlooked, is wine lees. These sediments settled at the bottom of the wine tanks at the end of the alcoholic fermentation process. Comprising approximately 10% of the total mass in wine production, wine lees have significant potential yet to be fully explored.
Wine lees are a rich mix of organic acids, carbohydrates, inorganic salts, proteins, phenolic compounds, grape plant residues, and yeast biomass. This complex chemical composition makes them a valuable source of useful compounds. Traditionally, under European regulation, their use has been confined to producing alcohol, spirits, and “piquette.” However, their potential applications have been extended.
Recent studies have explored the use of wine lees for various innovation purposes. They have been examined for their capacity to limit wine oxidation, enhance wine quality, and recover valuable compounds, such as phenolic substances and tartaric acid. The scope of their application ranges from additives in animal feed, ingredients in food formulation, and even forming the basis for creating nanomaterials.
However, the most intriguing aspect of wine lees is their role in winemaking. They are a valuable source of nutrients and protective compounds for lactic acid bacteria (LAB), which are crucial for conducting malolactic fermentation (MLF) in wines. Particularly, they are beneficial for strains such as Oenococcus oeni and, to some extent, Lactiplantibacillus. This blog delves into the innovative utilisation of wine lees, unfolding a narrative in which waste transforms into a vital contributor to the winemaking process, aligning with the goals of ecological sustainability and economic viability.
Wine lees, a by-product of the winemaking process, are emerging as a focal point in sustainable viticulture. These lees, which constitute the second most abundant byproduct of wine production after grape pomace, represent a significant portion of the total mass generated during winemaking (approximately 10 %). This sediment, composed of solid parts that settle at the bottom of wine tanks at the end of alcoholic fermentation, is more than just waste. It is a complex mixture of various substances that offers a plethora of potential applications.
The composition of wine lees is quite diverse and includes organic acids, carbohydrates, inorganic salts, proteins, phenolic compounds, plant residues from grapes, and yeast biomass used during the fermentation process. The specific makeup of these lees can vary significantly based on several factors, such as environmental conditions, agronomic characteristics of the grapes, grape variety, and winemaking practices, including techniques such as racking or duration of aging in wood barrels or tanks.
Traditionally, European regulations have limited the use of wine lees primarily to the production of alcohol, spirits, and “piquette.” However, the richness and complexity of their compositions open the door to various other valorisation strategies. With the increasing emphasis on sustainability and waste reduction in the wine industry, wine lees present an opportunity to explore new applications. These can range from their use in food and health products to their potential role in advanced material production.
Understanding the full potential of wine lees in sustainable practices not only offers economic benefits, but also aligns with the broader goals of ecological sustainability in the wine industry. As research continues to uncover new uses for these by-products, the traditional view of wine lees is shifting from waste material to a valuable resource, opening new avenues for innovation in winemaking and beyond.
This study bridges the gap between sustainable wine production and innovative winemaking techniques by exploring the use of white wine lees to stimulate lactic acid bacteria (LAB) growth and enhance malolactic fermentation (MLF) in wine. LAB, primarily Oenococcus oeni, play a crucial role in MLF, a secondary fermentation process that occurs in most red wines and in some white and sparkling wines. This process is vital for stabilising and enhancing the sensory qualities of wine, particularly its flavour and aroma profile.
Under normal circumstances, LAB spontaneously develop in wine during or after alcoholic fermentation (AF) and carry out MLF when they reach a sufficient population. However, the complex nutrient requirements of LAB, coupled with challenging conditions in wine, such as low pH and varying alcohol content, can hinder the successful completion of MLF. The use of selected LAB strains as starter cultures is a common winemaking practice for exerting better control over MLF. However, direct inoculation of these strains into wine can sometimes reduce their viability, thus jeopardising the MLF process.
The innovative aspect of this study lies in the application of wine lees, a byproduct of winemaking, to overcome these challenges. Yeast lees produced from different strains in a laboratory setting have demonstrated the potential to stimulate the activity of O. oeni, thereby facilitating MLF in synthetic wine. This positive effect is attributed to the increase in nitrogenous compounds and mannoproteins released by yeasts during winemaking. However, the extent to which wine lees obtained directly from winemaking can influence LAB growth, survival, and capacity to perform MLF remains largely unexplored. This study aimed to fill this knowledge gap by investigating the potential of wine lees, particularly white wine, to enhance MLF in red wines.
Research Methodology
The methodology employed in this groundbreaking study on the use of wine lees to promote the growth of lactic acid bacteria (LAB) and enhance malolactic fermentation (MLF) is innovative and meticulous. This research began with a preliminary assessment of the impact of wine lees on LAB growth. Specifically, we focused on the interaction between wine lees (labelled as lees 1) and Oenococcus oeni strain VF in a wine-like medium (WLM).
The WLM, prepared according to the guidelines established by Balmaseda et al. (2023), provides a controlled environment mimicking the conditions found in actual wine. This medium is critical for assessing the real-world applicability of the findings. The O. oeni VF strain was chosen for its relevance in the wine industry, especially in the MLF process. To evaluate the effect of wine lees on LAB growth, the O. oeni VF strain was inoculated into the WLM at varying concentrations – 10², 10⁴, or 10⁶ cells per millilitre. Concurrently, different quantities of wine lees (0, 0.25, or 0.5 grams per liter of lees 1) were added to observe their impact on LAB growth.
The inoculated WLM was then carefully transferred into 10 mL syringes equipped with hypodermic needles to maintain sterile conditions and allow for controlled environmental interactions. The syringes were incubated at a stable temperature of 20°C, which is a common temperature for wine fermentation. This setup allows researchers to closely monitor and control the experiment and ensure accurate and reliable data.
This methodology represents a fine balance between the laboratory precision and practical winemaking conditions. It was designed to closely replicate the actual environment in which wine lees and LAB interact during the winemaking process, thus providing valuable insights into how these interactions can be optimised in real-world scenarios.
Key Findings
The study’s examination of using white wine lees to enhance malolactic fermentation (MLF) in red wines offers insightful findings that could revolutionise the winemaking processes. This research primarily utilised freeze-dried white wine lees, focusing on their influence on lactic acid bacteria (LAB), particularly Oenococcus oeni, a key player in MLF.
One of the pivotal findings was that the presence of wine lees improved the performance of MLF. This was evident with three different commercial bacterial strains, where the addition of wine lees accelerated LAB growth kinetics compared to conditions without lees. Even in synthetic wines, where all strains completed MLF, irrespective of the presence of lees, the addition of wine lees enhanced the growth rate of LAB.
Furthermore, the study highlighted a linear relationship between the duration of MLF and the concentration of wine lees added to the wine. This finding was consistent across the different strains of bacteria used, reinforcing the hypothesis that wine lees can indeed enhance MLF under wine conditions. Higher concentrations of wine lees corresponded to shorter MLF durations, suggesting a dose-dependent response.
The researchers also explored the possibility of reducing the concentration of inoculated starter cultures in wine using wine lees. Tests conducted with lower initial bacterial populations (10² and 10⁴ cells/mL) showed that the addition of 0.25 g/L of wine lees could maintain the bacterial population for extended periods (up to 60 or 120 days), though this was not sufficient to achieve the minimal population needed for MLF. However, a higher concentration of 0.5 g/L of wine lees enabled a progressive increase in the bacterial population, eventually leading to the successful completion of MLF.
Another key observation was that the autolytic process of yeast lees, which occurs during wine aging, can influence the nutritional properties of wine lees. This process potentially affects the availability of certain compounds beneficial for LAB growth. Nevertheless, the overall results demonstrated that wine lees could effectively enhance O. oeni growth and improve the MLF performance in both synthetic and natural wines.
The study also established that the freeze-drying process used to preserve and store wine lees did not negatively affect their beneficial properties. The used concentrations of wine lees (0.25 g/L and 0.5 g/L) align with those of other oenological preparations, making them suitable for easy industrial adaptation. These findings present a promising outlook for using wine lees, a sustainable by-product, to enhance the efficiency and quality of the winemaking process.
Implications and Applications
The implications of this study’s findings are profound, especially in the context of sustainable winemaking and industrial applications. The observed enhancement of Oenococcus oeni growth and malolactic fermentation (MLF) performance in both synthetic and natural wine by the addition of wine lees represents a significant advancement in winemaking practices. The ability of wine lees to enable the completion of MLF in wines with low bacterial populations, which would otherwise fail to complete the process without their addition, is particularly noteworthy.
This study also underscores the viability of freeze-drying as a method for preserving and storing wine lees. This process does not diminish the beneficial effects of lees and offers a more manageable approach to dosage than fresh liquid wine lees. The concentrations of wine lees used in the study (0.25 g/L and 0.5 g/L) align with those of existing oenological preparations, suggesting that these findings can be readily adapted to industrial practices. This adaptability, combined with the sustainable nature of utilising by-products, such as wine lees, presents a compelling case for its broader application in the wine industry.
Conclusion
This study’s exploration of the use of wine lees in the wine industry, specifically for enhancing malolactic fermentation (MLF), has yielded several significant conclusions. First, the development of a new, low-cost culture medium comprising diluted grape juice and wine lees proved effective in producing the lactic acid bacteria (LAB) commonly used in MLF, such as Oenococcus oeni and Lactiplantibacillus plantarum. The efficacy of this medium, with 100 mL/L grape juice and 10 g/L freeze-dried wine lees, was demonstrated by its ability to produce up to 10 °C CFU/mL.
Second, this study confirmed that the addition of wine lees could effectively reduce the duration of MLF in wines with high bacterial populations (>10⁴ cells/mL), while simultaneously enabling sufficient bacterial growth to complete the fermentation process. This finding has practical implications for enhancing the efficiency of winemaking processes.
Third, the addition of wine lees positively influenced the quality of the volatile composition of wine. Notably, it increased the concentrations of certain esters, which are crucial in the development of fruity aromas characteristic of red wines.
Lastly, the study established that the addition of wine lees did not promote the growth of spoilage microorganisms such as Brettanomyces bruxellensis. This aspect is particularly important because it ensures that the quality and safety of the wine are not compromised.
In summary, this integrative study suggests that wine lees can be effectively used as LAB growth activators in winemaking without posing a risk of microbial spoilage or compromising the aromatic quality of the wine. These findings represent a significant step forward in sustainable winemaking, proposing the innovative use of a by-product that has traditionally been undervalued.
Please read all in: Balmaseda A, Miot-Sertier C, Lytra G, Poulain B, Reguant C, Lucas P, Nioi C. Application of white wine lees for promoting lactic acid bacteria growth and malolactic fermentation in wine. Int J Food Microbiol. 2024 Jan 19;413:110583. doi: 10.1016/j.ijfoodmicro.2024.110583. Epub ahead of print. PMID: 38277869. https://doi.org/10.1016/j.ijfoodmicro.2024.110583